This invention is directed to a novel hydroxy-functional polyester and more specifically to an acrylic-modified hydroxy-functional polyester useful as a diluent with a wide variety of thermoplastic or thermosetting paint vehicles. More specifically, this invention is directed to hydroxy-functional polyester diluents and acrylic-modified hydroxy-functional polyester diluents useful with a wide variety of thermoplastic or thermosetting polymeric film-forming polymers.
The thermoplastic and thermosetting film-forming vehicles or polymers such as the polyurethanes, alkyds, acrylics, and polyesters are well-known as vehicles for coating compositions and have been applied on a variety of substrates. The formulation of these vehicles in coatings can be varied to optimize the desired performance characteristics. However, in some instances optimizing one characteristic can adversely effect the other desirable characteristics required of a particular coating. For example, in refinishing automobile or truck bodies a variety of thermoplastic and thermosetting film-forming polymers are used and include such polymeric vehicles as the acrylic lacquers and enamels, the nitrocellulose lacquers, the alkyd enamels, the polyester enamels, the polyurethane enamels and the like. These vehicles must have sufficient flexibility for application to various substrates, i.e. metal parts, but may not be sufficient for the more flexible plastic materials utilized in today's automobile and truck bodies.
The hydroxy-functional polyester diluents, including the acrylic-modified polyester diluents of this invention have excellent compatibility with a wide variety of film-forming polymers and are particularly adaptable for use as automotive topcoats. Upon curing, these coatings form a glossy durable finish, exhibit excellent adhesion to metal with superior pigment dispersibility and are resistance to solvents. The preferred coating can be formulated to contain more than about 75%, e.g. up to about 90%, by weight of non-volatile solids. Because of the strict solvent emission regulations of recent years, low solvent emission coatings have become very desirable and a number of low VOC paint compositions have been proposed to meet these requirements. However, many of the available coatings are deficient in this regard because of the difficulty in application, adhesion, lack of flexibility, poor durability, poor pigment dispersibility and low solvent resistance. Therefore, many of these coatings are deficient for use as automotive topcoats, especially when the topcoat includes a metallic flake as the pigment. The low viscosity of these coatings are not sufficient to immobilize the flakes which tend to redistribute and thereby give a nonuniform distribution in the film. The coatings of this invention, however, combine the desired characteristics, e.g. good pigment dispersibility, etc., with the low application viscosity and are therefore particularly adaptable for automotive and truck body topcoats including coatings which use metallic flakes as the pigment.
The prior art required the use of mixtures of polyisocyanates with polyesters such as disclosed in U.S. Pat. No. 4,451,600 and U.S. Pat. No. 4,419,293. These additives, however, are not adequate for preparing coatings comprising polymeric low volatile organic compound (VOC) compositions adapted for use as automotive topcoats. Moreover, the coating compositions of this invention are capable of being cured at ambient temperatures, i.e. low bake and can be used in combination with a variety of pigments, including metallic flakes. Thus, the coating compositions of this invention have more than about 75% by weight of nonvolatile solids exclusive of the pigment and other nonreactive components and comprise a low molecular weight polyester with pendent hydroxy-functional groups and polymerizable double bonds and have a number average weight ranging up to about 500 and more likely in the range of 140 to 300.